With the arrival of static electronic electricity meters, the question arises as to how dependable these meters are without maintenance over decades. Since the failure rate of these meters is roughly proportional to the number of electronic components, it is advisable to use as few electronic components as possible for the metering of electricity usage.
Meters for measuring electrical current consumption often incorporate current transformers or shunts. The use of shunts is generally practical only for one-phase alternating current meters. In the case of three phase electricity meters, galvanic separation of the circuits from one another proves to be necessary, so that one use of a current transformer is usually required. With the use of such transformers, one problem is magnetic saturation incidents, i.e. overloads of the transformer core. Such magnetic core saturation incidents lead to under measurement of energy consumption. Saturation incidents arise from excess currents and from D.C. components in the current, formed for instance by one way rectification. There are so called active current transformers with electronic auxiliary current circuits which make sure that a saturation of the transformer core is avoided. Such active current transformers have the disadvantage that they increase the complexity of the electronic meter. This increases the failure rate and reduces the length of time the electronic meters may be used.
Direct current components in the consumer current circuit of utility company electricity customers normally occur in connection with the intended stealing of electricity. I.e., if the use of direct current components could be excluded, then the classical passive current transformers (rather than the aforementioned active current transformers) would be sufficient. Thus the question arises, if it is necessary and economically sensible to equip all static electricity meters that are supposed to be installed in the network with the relatively complex active current transformer. Such active current transformers decrease the standard time of validity of the calibration of the meter and are insensitive to direct current. Alternatively, one may look for ways to detect the few customers that take substantial direct current out of the network.